test(verify): run a Python operator the way the engine runs it

[kz930]

What changes were proposed in this PR?

A Python operator is not called; it is handed to an interpreter that imports
the generated module and drives it through the same open, process and close
the engine uses. PyOpExecHarness writes that module, starts the driver, and
reads back what the operator emitted.

The driver is the engine's side of the contract written out plainly: it is
what makes the answer this side produces the engine's answer rather than an
approximation of it.

Eight lines of build.sbt are unrelated to the export and fixed while this change is in the file: File Service's test grouping read its fork options inside the lambda, which sbt hoists anyway, so the warning it printed on every build said the code meant something it did not.

Any related issues, documentation, discussions?

Part of #8325, 3 of 20; that issue lists the set in order.

How was this PR tested?

The tests in this change cover it. The whole set is exercised together once the last piece lands: every operator run through the engine and through its generated script, and the two answers compared.

Was this PR authored or co-authored using generative AI tooling?

Generated-by: Claude Code (Opus 5)

[github-actions]

Automated Reviewer Suggestions

Based on the git blame history of the changed files, we recommend the following reviewers:

• Contributors with relevant context: @mengw15
  You can notify them by mentioning @mengw15 in a comment.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.10%. Comparing base (7976744) to head (4659852).
⚠️ Report is 10 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8357      +/-   ##
============================================
- Coverage     94.11%   94.10%   -0.02%     
- Complexity     4811     4858      +47     
============================================
  Files          1197     1203       +6     
  Lines         48813    48967     +154     
  Branches       5906     5930      +24     
============================================
+ Hits          45939    46079     +140     
+ Misses         1420     1419       -1     
- Partials       1454     1469      +15     

Flag	Coverage Δ		*Carryforward flag
access-control-service	81.00% <ø> (ø)
agent-service	99.32% <ø> (ø)		Carriedforward from d2e8495
amber	90.08% <ø> (ø)		Carriedforward from d2e8495
computing-unit-managing-service	73.67% <ø> (ø)
config-service	87.12% <ø> (+0.12%)	⬆️
file-service	87.91% <ø> (ø)
frontend	96.86% <ø> (ø)		Carriedforward from d2e8495
notebook-migration-service	83.57% <ø> (+4.26%)	⬆️
pyamber	98.47% <ø> (ø)		Carriedforward from d2e8495
workflow-compiling-service	77.19% <ø> (ø)		Carriedforward from d2e8495

*This pull request uses carry forward flags. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[github-actions]

⚠️ Benchmark changes need a look

🟢 0 better · 🔴 15 worse · ⚪ 0 noise (<±5%) · 0 without baseline

CI benchmark results are noisy; treat <±5% as noise unless repeated.

Dashboard · Run

	config	throughput	MB/s	latency	max Δ latest / 7d
🔴	bs=10 sw=10 sl=64	376	0.229	25,649/34,091/34,091 us	🔴 +114.8% / 🔴 +113.3%
🔴	bs=100 sw=10 sl=64	782	0.477	126,864/156,342/156,342 us	🔴 +57.2% / 🔴 +43.1%
🔴	bs=1000 sw=10 sl=64	901	0.55	1,104,890/1,214,223/1,214,223 us	🔴 +27.8% / 🔴 +16.4%

Baseline details

Latest main cd4fd5a from 2026-09-03T13:02:32.113Z

config	metric	PR	latest main	7d avg	Δ latest	Δ 7d
bs=10 sw=10 sl=64	throughput	376 tuples/sec	791.1 tuples/sec	755.36 tuples/sec	-52.5%	-50.2%
bs=10 sw=10 sl=64	MB/s	0.229 MB/s	0.483 MB/s	0.461 MB/s	-52.6%	-50.3%
bs=10 sw=10 sl=64	p50	25,649 us	12,219 us	12,938 us	+109.9%	+98.2%
bs=10 sw=10 sl=64	p95	34,091 us	15,867 us	15,980 us	+114.8%	+113.3%
bs=10 sw=10 sl=64	p99	34,091 us	18,101 us	19,233 us	+88.3%	+77.3%
bs=100 sw=10 sl=64	throughput	782 tuples/sec	1,082 tuples/sec	976.3 tuples/sec	-27.8%	-19.9%
bs=100 sw=10 sl=64	MB/s	0.477 MB/s	0.661 MB/s	0.596 MB/s	-27.8%	-20.0%
bs=100 sw=10 sl=64	p50	126,864 us	90,900 us	102,340 us	+39.6%	+24.0%
bs=100 sw=10 sl=64	p95	156,342 us	99,461 us	109,262 us	+57.2%	+43.1%
bs=100 sw=10 sl=64	p99	156,342 us	105,783 us	118,827 us	+47.8%	+31.6%
bs=1000 sw=10 sl=64	throughput	901 tuples/sec	1,108 tuples/sec	1,006 tuples/sec	-18.6%	-10.5%
bs=1000 sw=10 sl=64	MB/s	0.55 MB/s	0.676 MB/s	0.614 MB/s	-18.6%	-10.5%
bs=1000 sw=10 sl=64	p50	1,104,890 us	902,554 us	999,855 us	+22.4%	+10.5%
bs=1000 sw=10 sl=64	p95	1,214,223 us	949,861 us	1,042,833 us	+27.8%	+16.4%
bs=1000 sw=10 sl=64	p99	1,214,223 us	985,895 us	1,070,722 us	+23.2%	+13.4%

Raw CSV

config_idx,batch_size,schema_width,string_len,num_batches,total_ms,total_tuples,total_bytes,tuples_per_sec,mb_per_sec,lat_p50_us,lat_p95_us,lat_p99_us
0,10,10,64,20,532.40,200,128000,376,0.229,25649.22,34091.03,34091.03
1,100,10,64,20,2557.40,2000,1280000,782,0.477,126863.98,156342.01,156342.01
2,1000,10,64,20,22191.97,20000,12800000,901,0.550,1104890.40,1214223.49,1214223.49